Method for preventing plastic from hardening in a dispenser tip

ABSTRACT

A method for preventing hardening of plastic material in a dispenser tip during periods of nonuse of the dispenser tip. The method involves providing a balloon around the dispenser tip, and then filling the balloon with plastic material.

BACKGROUND OF THE INVENTION

Flowable plastic materials are commonly used in manufacturing processesas sealants and adhesives. For example, a single component polyurethaneadhesive-sealer is commonly applied around the periphery of windshieldglass to provide a sealant and adhesive. The material is applied as abead. The commonly used polyurethanes cure at room temperature to arubber-like consistency. The curing is caused by reaction with moisturein the air.

The plastic material is frequently dispensed as a bead from automaticdispensing machinery. Such dispensing machinery employs a nozzle-likedispensing tip connected to a plastic material source. During usage ofthe dispensing machinery, material is purged frequently enough toprevent hardening of the material in the dispensing tip and the arearearward thereto. However, during periods of non-use, such as may occurovernight, on weekends, during plant shut-downs and the like, materialis not dispensed from the dispenser tips. If material is not frequentlydispensed from the dispenser tip, it can harden in the passage of thedispenser tip and plug the dispenser tip and perhaps passagewaystherebehind. In order to prevent this from occurring, the dispenser tiphas been purged at regular intervals during periods of non-use byforcing plastic material therethrough even though the material is notused. This material is lost by dumping it into a drum or othercontainer. This is, of course, an expensive proposition.

In accordance with the present invention, a method is provided toprevent hardening of the plastic material during periods of non-use ofdispensing machinery.

SUMMARY OF THE INVENTION

A method for preventing flowable plastic material of the type whichcures in the ambient atmosphere from hardening in a dispenser tip duringperiods of non-use is provided. The method includes the step of firstproviding an elastomeric balloon having an expandable main body portionand an expandable hollow neck communicating therewith. The neck ismounted on a dispenser tip with the dispenser tip extending into themain body of the balloon. Then flowable plastic material is dispensedfrom the dispenser tip into the main body until the main body is filledwith the outer end of the dispenser tip being encased within the plasticmaterial.

IN THE DRAWING

FIG. 1 is a diagrammatic view of dispensing machinery in accordance withwhich one embodiment of the present invention is used;

FIG. 2 is an elevational view of a dispenser tip with a balloon mountedthereon;

FIG. 3 is a view similar to FIG. 2 with the main body of the balloonfilled with plastic material; and

FIG. 4 is a sectional view illustrating the condition of the plasticmaterial within the balloon after the material has cured to some extent.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring to FIG. 1, it will be noted that plastic dispensing machinery10 includes a dispenser tip 12. The dispenser tip 12 is a hollownozzle-like element usually fabricated of a plastic material. Enlargedhead 14 is secured to the outlet from the dispensing machine 10. Thedispenser tip 12 terminates in an open end 16. A V-shaped notch 18 isprovided in the end 16 to facilitate the proper shape of a bead of thedispensed material being formed on a piece, such as the periphery ofwindshield 5. glass. The dispenser tip 12 is connected to a supply offlowable plastic 20 via line 22 which may have, for example, a valve 24and pump 26 therein. The flowable plastic material is usually in aviscous condition. The material may be, for example, a polyurethanewhich cures to a rubber-like consistency when exposed to the ambientatmosphere.

The dispenser tip 12 is frequently mounted on a robot. The robot movesthe dispenser tip 12 around the periphery of windshield glass or otherstructure to provide a bead of urethane. The urethane functions as asealant and adhesive.

In order to prevent hardening of the plastic material during periods ofnon-use of the dispenser tip 12, the method of the present invention isemployed.

Firstly, an elastomeric balloon 28 having an expandable main body 30 andan expandable open-ended hollow neck 32 communicating therewith isprovided. The balloon may be fabricated of rubber or a suitable plastic.When it is desired to deactivate the dispenser tip 12, the neck 32 ismounted on the dispenser tip 12 with the dispenser tip 12 extending intothe main body 30 of the balloon 28.

After the balloon 28 has been mounted, flowable plastic material isdispensed by means of the dispensing machinery 10 through the dispensertip 12 into the main body 30 of the balloon 28 until the main body 30 isfilled as illustrated in FIG. 3. The elastomeric nature of the balloon28 permits expansion of the main body so that it is assured that themain body 30 is filled as illustrated. Air present in the balloon isforced radially outwardly during the filling process. The outer end 16of the dispenser tip 12 is encased within the plastic material 34 asillustrated in FIG. 4.

After a period of time, the radially outward portion of the plasticmaterial 34 will cure forming an outer layer 36 of the plastic material34. The layer 36 forms a protective outer shell sealing the center orcore portion 38 from the ambient atmosphere and preventing curingthereof. The curing is a consequence of the ambient atmosphere which ispresent radially outwardly of the balloon 28 interior. As mentioned, theair is forced outwardly during the step of filling the balloon. However,the curing process terminates because of the limited amount of air andthe center or core 38 will remain in a flowable viscous state for arelatively long time. Thus, as long as the balloon 28 remains on thedispenser tip 12, the plastic material 40 in the passageway 42, definedby the dispenser, tip 12 is inhibited from curing.

We claim:
 1. The method for preventing flowable plastic material of thetype which cures when exposed to air from curing in a hollow tubulardispenser tip during periods of extended non-use of the dispenser tipcomprising the steps of:a. providing an elastomeric balloon having anexpandable main body portion and an expandable open-ended hollow neckcommunicating therewith; b. mounting the neck on a dispenser tip withthe dispenser tip extending into the main body of the balloon; c.dispensing flowable plastic material from the dispenser tip into themain body thereby forcing the air therewithin radially outwardly; d.continuing said dispensing of flowable plastic material until the mainbody is substantially filled with the outer end of the dispenser tipencased within the plastic material; and e. curing the radially outwardportion of the plastic material by means of the air trapped in the mainbody to form a protective outer shell sealing the center portion fromthe ambient atmosphere and inhibiting curing thereof.